1. Field of the Invention
This invention relates to a private branch exchange apparatus and particularly to a private branch exchange apparatus with a function for providing selective services to a push button telephone connected thereto with additional functions and to a general telephone without additional functions connected thereto in parallel to the push button telephone.
2. Description of the Prior Art
A private branch exchange apparatus is known. Such a prior art private branch exchange apparatus is connected to a plurality of push button telephones to provide communication with a telephone line and intercommunication between the push button telephones connected thereto. The prior art private branch exchange apparatus comprises extension ports, each having a speaking circuit for transmitting voice signals and a data communication circuit for communicating data, for example, information of ON HOOK or OFF HOOK, ring command data, or the like. A plurality of push button telephone are connected thereto to provide users various additional functions with the private branch exchange apparatus.
Another prior art private branch exchange apparatus referred to as a hybrid type electronic private branch exchange apparatus is known. Such a prior art private branch exchange apparatus has an external port capable of connection to both a push button telephone and a general telephone having only basic function in parallel.
However, in the prior art hybrid private branch exchange apparatus, there is a problem that when a call reaches to one of extension ports of the hybrid private branch exchange apparatus, both push button telephone and general telephone ring at the same time. That is, it is impossible to selectively ring either of them. Moreover, there is a problem that it is impossible for either of the push button and general telephone connected to the same extension port to call the other one by using ringing.